Polaris Water Heater Blower

A few weeks ago I started hearing a bearing squeal in the blower motor on our Polaris heater and decided to replace it. What I did not know is that the motor is not sold separately, it comes as a "blower assembly". Once I realized that the propane flows through the blower housing I understood why.

My problem is that, after spending several hours swapping our the blowers, the new one has vibrations and noise. I removed the assembly and ran it to find that there are no balance problems and all was quiet. After reinstalling and making sure the mounting bolts were torqued properly and gaskets installed correctly, I still have noise.

I have not checked to see if there is an obstruction in the air intake pipe and plan on doing that today. Other than an obstruction which would cause a load on the blower, I am not sure what else to check.

Also, I could not figure out the purpose of the "Blower Housing Switch", a micro switch which contacts the blower housing. The switch is normally open and has to be pressed against the housing cover to close it. The steel cover is too rigid to deflect so the only purpose I can imagine is to cut off power if the blower should come loose at the mounting bolts.